Side-by-side ambient comparison of Capture vs

Standard Vaporizer

Weiwei Hu, Pedro Campuzano-Jost, Doug Day, Jose L. Jimenez, Phil Croteau, and John T. Jayne

University of Colorado-Boulder & Aerodyne Research

7-Sep-2013: AMS Users Meeting, Prague(Analysis still preliminary)

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Motivation: Field Comparison of OA for 3 AMSs + 1 ACSM (all standard vaporizer)

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So just compare the AMS w SMPS!

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Experimental Setup

HR-AMS 2STD

VAPORIZER,ePToF

HR-AMS 1Capture

VAPORIZER

CU Roof

10 lpm

1.2 lpm

0.6 lpm

0.6 lpm

5 min V5 min W

5 min V/PToF5 min V/ePToF

Both AMS were AN, AS and size calibrated before the comparison

Capture Vaporizer was being run at 4 W, PToF sample time ~ 1 min/5 min cycle

Dry (< 15% RH)

CE = 0.5 for Std vaporizer (per Middlebrook et al., AS&T 2012)

John Jaynes’s presentation forePToF results

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Time Series of Main Species

Using measured IE, NH4 RIE and SO4 RIE on each vaporizer

Fresh Plumes Period, CE=1 was applied to Org in standard Vaporizer

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CaptureStandard

Species scatter plots

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Cap

ture

Standard

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Tge

Monodisperse NH4NO3 in PToF

Capture vaporizer has delayed signals (e.g 30 s for 400 nm), and broader peaks

Capture

Standard

Monodisperse (NH4)2SO4 in PToF

The size distribution of pure (NH4)2SO4 in the capture vaporizer was broadened due to the longer vaporization time. 8

Capture

Standard

Ambient size distribution: Std vs captureShifting the standard vapPToF by 500 us makes the high volatity species (AN) collapse on top of each other. So while delayed and slightly smeared, PToFseems useful!

Warning: Slightly unfair comparison 1% chopper (capture vap) vs ePToF (standard vap)9

CaptureStandard

Sulfate Fragmentation

• Only SO2+ & SO+

• SO2+/SO+ ratio slightly larger 10

CaptureStandard

Nitrate Fragmentation

While detecting RONO2 with the capture vaporizer is not impossible, at ambient concentrations it might be quite challenging… 11

CaptureStandard

HR average spectra (Normalized to 1)

More small fragments (e.g m/z 28, 40, 44) in capture vaporizer, and less higher m/z 12

Capture

Standard

Capture - Standard

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HR Spectra of Fresh “Cooking” Plumes

Capture

Standard

Capture - Standard

f44 comparison and Sally’s Triangle

• f44 is probably still an O/C proxy but some new complications, may need replacement for f43

• m/z 40 and 55 can be enhanced, so possibly we can use those instead 14

f 44

Cap

ture

f44 Standard

Standard

Capture

Nominally higher O/C and lower H/C w/ capture vap.

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Still shows the same evolution Need to re-calibrate the elemental analysis

Capture

Standard

CO+/CO2+ & H2O+/CO2

+

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Cap

ture

Stan

dard

V

Cap

ture

Stan

dard

W

Frag

Tab

le

Stan

dard

V

Stan

dard

W

Frag

Tab

le

Biomass Burning Tracer f60

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Capture

Standard

Non-BB background

Non-BB background

PMF Comparison

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CaptureStandard

Spectra of OA PMF factors

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CaptureStandard

Time series of PMF OA factors

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CaptureStandard

Conclusions• Capture vaporizer works, CE ~1 !

• Need to recalibrate RIEs, O/C…• Slower evaporation, PToF ok for ambient• MS shifted to smaller fragments

• Still see same trends in VK diagram, Sally’s triangle

• Much higher signal at CO2+, H2O+

• Seem to lose f60, organic nitrates• Other tracers may still be usable

• Additional testing for SOAS, to be analyzed21